Infectious diseases caused by viruses, such as influenza, are prevalent every year. As a means for preventing such infectious diseases or severe conditions, a vaccine, in which an antigen such as an attenuated virus or an attenuated virus-derived fragment is administered into a living body to provoke an antigen-specific immune response, has been developed. Moreover, from the viewpoint of prevention, in recent years, a vaccine comprising a cancer antigen or a dementia antigen has also been developed. However, with regard to the effectiveness of such vaccines, if such an antigen alone is administered, it hardly exhibits sufficient effects. Thus, a substance that enhances antigenicity, which is called adjuvant, needs to be simultaneously administered. Meanwhile, such an adjuvant has been problematic in terms of side effects, and thus, has been worried about its safety for a long period of time. Under such circumstances, competition for the development of a safe and highly efficient adjuvant has been intensifying over the world. To date, a large number of lactic acid bacterium species having immunopotentiating effects have been known, and they do not have almost no safety concerns. Thus, such lactic acid bacterium species having immunopotentiating effects have been applied to many food and drink. Among such lactic acid bacterium species, Lactobacillus plantarum Strain AYA (see Patent Literature 1), Lactobacillus pentosus ONRIC b0240 (see Patent Literature 2), Lactobacillus balgaricus OLL1073R-1 (see Non Patent Literature 1), etc. have been known as lactic acid bacterium species that increase the amounts of antibodies specific to antigens. At present, vaccines distributed over the world have two expected effects. Specifically, one effect is induction of an antigen-specific antibody via B cells, and the other effect is induction of antigen-specific cytotoxic T lymphocytes (CTL). The former plays a role in removing the source of infection and/or an antigen that have entered a living body, whereas the latter plays a role in removing infected cells and/or antigen-expressing cells from the living body. Hence, it is important that the antibody and CTL act in a coordinated manner. However, there have been no reports regarding a lactic acid bacterium that enhances the amounts of both antigen-specific cytotoxic T lymphocytes (CTL) and antigen-specific antibodies, which are considered most important for protection against viral infection, when the lactic acid bacteria are orally administered. In view of the foregoing, it has been desired to develop a substance and a method for enhancing antigenicity by oral ingestion, which have both effectiveness and safety.